A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide.
Intergranular Stress Corrosion Cracking (IGSCC) is a known phenomenon occurring in reactor components, such as structural members, shrouds, piping, fasteners, and welds, exposed to stress in a corrosive environment. Typically, IGSCC initiates from a crevice at the base material along a weld in what is referred to as the heat affected zone. Reactor components are subject to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to IGSCC.
Over the life of the reactor, the shroud is often inspected to verify integrity. For example, the shroud welds must be periodically inspected for Intergranular Stress Corrosion Cracking (IGSCC). Such inspections are typically performed with ultrasonic transducer type inspection tools. Based upon such inspections, the shroud may require either repair or replacement. It is sometimes necessary to supplement the data obtained by the primary inspection tooling to increase the volumetric coverage of circumferential welds of the shroud before the decision to repair or replace can be made.
It would be desirable to provide a compact, easy to use, supplemental, automated, ultrasonic inspection system to enhance the percentage of volumetric weld coverage. It would also be desirable to provide a supplemental inspection tool that can be delivered to the appropriate weld location by a handling pole from the refueling platform of the reactor. It would further be desirable to provide such an apparatus that is operated remotely from adjacent the reactor cavity.